Relay with time delay coil

ABSTRACT

An electromagnetically operated A.C. relay which is actuated an adjustable timed interval after the relay is energized. The relay incorporates the timing accuracy provided by a solid state timing circuit and the power switching advantages provided by mechanically operated switching contacts. The relay includes a unitary coil and timing unit which may be substituted for a coil in an instantaneous operated relay to convert the instantaneous operated relay to a relay which is actuated a predetermined time interval after the relay is energized.

United States Patent Boleyet al.

[111 3,824,434 1 51 July '16, 1974 RELAY WITH TIME DELAY COIL OTHERPUBLICATIONS 1 Inventors: Q f Boley, Lexington, y- The Class 8501. Typeor Solid State Timer, Timing al s Whltefish Relays, Square D Company,Bull. SM32l FAK, H64,

[73] Assignee: Square D Company, Park Ridge, lll.

- Primary Exammer.lames D. Trammell [22] Flled: 1972 Attorney, Agent, orFirm-William H. Schmeling; [2| Appl. No.: 318,053 Harold Rathbun 2 Cl 57I ABSTRACT 51% Fits}?! 3 l7/l4IlI0S1,h3i;/?; An electlromagneticrauyOperate-d A'C. relay whicfi is, [58] Fie'ld 67 202, actuated anadjustable timed intervalafter the relay is a 1 41 energized. The relayincorporates the timing accuracy provided by a solid state timingcircuit and the power switching advantages provided by mechanicallyoper- [56] References Cited ated'switching contacts. The relay includesa unitary UNITED STATES PATENTS coil and timing unit which may besubstituted for a 3,501,723 3/ 1970, Marien 335/202 coil in aninstantaneous operated relay to convert the 3,558.996 H1971 Mitchell etal. 317/141 S instantaneous Operated relay to a relay which is actu-$562,595 M971 swfmson 317/141 5 .ated a predetermined time intervalafter the relay is 3,641,397 2/1972 Ell1otetal.....-. 3l7/l4l Senergized 3,683,301 8/l972 Boley et al..- 335/59 3,688,130 8/1972Granieri 317/141 S 10, Claims, 5 Drawing Figures 3O 7 1 J2 ill I m 66 7O72 32 no 4e 28 l v RELAY WITH TIME DELAY COIL This invention relatestoelectromagnetically operated switching devices and is more particularlyconcerned with a device having an alternating current magnet which isenergized a predetermined time interval after power is applied to acontrol circuit of the device.

Timing devices are frequently used in industrial equipment to controlanoperating interval of a machine function or a process step as well asprovide an output signal if an anticipated event fails to occur within aprescribed time interval. One form ofa timing device frequently used inindustrial installations is known as a pneumatic timer, an example ofwhich is illustrated in US. Pat. No. 2,929,898, which was granted toCarl A. Schaefer on Mar. 22, 1960. While timers as shown in the Schaeferpatent have been used with success in industry, their accuracy generallyis limited when timing prolonged time intervals and their function maybe impaired by dusty or highly corrosive environments. Another form oftiming unit, which has been more recently introduced, is a device knownas a solid state timer which uses solid state circuitry to measure atime interval and solid state components, such as silicon controlledrectifiers, to control the opening or closing of an output circuit.While solid state timing devices maybe constructed to accurately timeprolonged timing periods and to be unaffected by substantially allenvironments', their use is restricted inthat they are usu allyexpensive and limited because of the heat sinks which are required todissipate the heat generated in the solid state components by currentsin the output circuit. Another form of a timing device is disclosed inUS. Pat. No. 3,683,301 which was granted to the inventors Robert D.Boley, Charles F. Meyer, Rudolf H. Kiessling and Kenneth L. Paape onAug. 2, 1972. While the timing device as shown in the Boley et al patentincorporated the advantages of both pneumaticand solid state timingdevices, it included a complicated latch mechanism and was capable ofswitching only a limited number of power circuits. The timing device aswill be hereinafter'described incorporates the advantages of bothpneumatic and solid state timing devices in that it will provideaccurately timedperiods and is capable of switching the same number ofcircuits and has the same voltage clearances as required by industrystandards as a relay, the parts of which form the basic structure of thedevice.

It is an object of the present invention to provide a replacement coilassembly in an alternating current type relay which will cause the relayto actuate its switching contacts an adjustable timed interval after thecoil assembly is energized.

Another object is to provide a coil assembly in anelectromagneticallyoperated device which will cause the device tooperate its switching contacts a predetermined time interval after thecoil assembly is energized.

' An additional object is to, provide a replacement coil assembly for acoil of an AC. relay so the relay will operate with a timed delay afterthe coil assembly is ener gized with the assembly including a coilwinding and a circuit having solid state components which will delay theenergization of the coil for an adjustable timed interval after analternating current is supplied to a pair of input terminals of theassembly.

Further objects and features of the invention will be readily apparentto those skilled in the art from the following specification and fromthe appended drawings illustrating certain preferred embodiments inwhich:

FIG. 1 is a front view in elevation of an electromagnetic switchincluding a coil assembly according to the present invention;

FIG. 2 is a cross-sectional view taken along line 22 in FIG. 1;

FIG. 3 is a cross-sectional view of the coil assembly in FIG. I; v v

FIG. 4 is a front view of the coil assembly in FIG. 1 with a cover foran external resistor removed; and

FIG. 5 is a schematic diagram of a circuit controlling the energizationof a coil winding according to the present invention. I

An electromagnetic switch or relay 10, as shown in the drawings, isidentical with an electromagnetic relay as disclosed in US. Pat. No.3,501,723, which was granted to Kenneth J. Marien on Mar. 17, 1970 andassigned to the assignee of the present invention, with the exceptionthat the coil for the electromagnet in the relay shown in the Marienpatent is replaced by a coil assembly 12 in the relay 10. As theconstructional details of the relay 10 are fully disclosed in the Marienpatent, only a brief description necessary to understand thepresentinvention will beset forth herein, it being understood that theinvention disclosedhcrein may be used with electromagnetic devices otherthan shown in the Marien'patent.

'The relay 10 includes a base 14 which is formed as a unitary part ofdie cast metal material and has openings 16 which receive screws formounting the relay 10 on a panel. Positioned at a top portion of thebase 14 by suitable screws 20 is an insulating support 22 carrying a rowof spaced pairs of stationary contacts, each designated by a numeral 24.The respective pairs of stationary contacts 24 are located to be bridgedby individual movable contacts 26 which are resiliently supported bysprings and movable contact retainers on a movable contact carrier 28.The structure of the support 22, the stationary contacts 24, the movablecontacts 26, the carrier 28, are more fully disclosedand described inUS. Pat. No. 3,501,717, which was granted to the inventors Allin -W.Schubring and Kenneth L. Paape on Mar. 17, 1970 and assigned to theassignee of the present invention.

An electromagnet assembly, which when energized causes the movablecontact carrier 28 to move upwardly on the base 14, includes astationary magnet 30, a movable magnet part or armature 32, and the coilassembly 12. The magnet 30 includes a stack of E-shaped magnet ironparts which are laminated upon each other and tightly held assembledbetween a pair of magnetic E-shaped side plates by rivets. The magnet 30has a pair of spaced arms extending downwardly from opposite ends of abody portion 38 with a central leg extending from the body portion sothat the spaced arms are spaced on opposite sides of the central leg.The spaced v i The coil assembly 12 includes a molded shell 48 and amolded housing 50. The shell 48 has a cavity 52 extending from an opentop end. A coil winding 54 surrounds a'projection 56 that extendsupwardly in the cavity 52 from the bottom side of the shell 48. Theprojection 56 has a rectangular opening 58 which receives the centralleg of the magnet'30 while the spaced arms of the magnet 30 extend alongthe opposite sides of the shell 48 so that portions of the coil winding54 are located between the central leg on the magnet 30 and the spacedarms. The cavity 52 is filled with a suitable epoxy type encapsulatingmaterial after the coil 54 is positioned in the cavity 52.

The housing 50 includes a top wall 60, side walls 62,

a bottom wall 64 and a front wall 66 whichdefine a cavity 68 havinganopen rear side which is closed by a front end wall 70 on the shell 48,when the shell 48 and housing 50 are secured together by a pair ofscrews 72 located'at diagonally opposite corners of the wall 70.Positioned on the front wall 66, so as to be externally accessible, area pair of terminals 74a and 74b, a lens 76 and an adjustment knob of apotentiometer resistor 78. Extending in the top wall 60 and the frontwall 66 is an alcove 80. A resistor 82 is positioned in the alcove 80and a metal cover 84 is positioned to cover the alcove 80.'The cover 84is secured on the housing 50 by an opening 86 in the cover 84 whichreceives a boss 88 on the front wall 66 and an apertured ear 90 whichreceives one of the screws 72. The terminals 74a and 74b are positionedon the front wall 66 by screws 92 which extend through suitably locatedopenings in-the-front wall and arethreaded into portions of theterminals 74a and 74b respectivelythat are located in the cavity 68.Positioned within the cavity 68 by resilient pads is a thick-filmsubstrate board 98, preferably formed of alumina which provides amounting for the circuit and components shown in FIG. with the exceptionof theresistor 82 and potentiometer resistor 78. The activecomponents,i.e., transistors, triacs and capacitors, are mounted on thefront sideof the substrate 98 and the resistors and conductive circuitryare printed on the rear side of the substrate 98 by thick filmtechnology in a manner 'well known to those skilled in the art. Thewinding of the coil 54 is connected to the circuit on the "rear side ofthe substrate'98 by a pair of leads 100 and l00a..The potentiometer 78,the resistor 82' and the portions of the terminals 740 and 74b areconnected'to the circuit on the front side of the substrate 98 by pairsof leads l02a-b, 104ab and l06a-b, respectively. The coil assembly 12,the magnet 30, and the armature 32 are assembled in the switch in amanner described in the Marien patent. During assembly of theelectromagnet, the magnet 30 is positioned so its central leg isreceived in the opening 58 from the top side of the coil assembly 12 andthe armature 32 is positioned's'o its central leg extends in the opening58 from the bottom side of the coil assembly 12 while the electromagnetassembly is detached from the base 14. The electromagnet assembly isthen positioned on the base 14 to have a mounting screw 108 extendingthrough a bore in the body portion 38 aligned with the threaded openingin the base l4 and a bore in the body portion 46 aligned to receive apin 110 that extends from the movable contact carrier 28. Theelectromagnet assembly is maintained in its position by tightening thescrew 108. The removal of the electromagnet as sembly is accomplished bymerely looseningthe screw 4 108 and lifting the electromagnet assemblyfrom its position on the base 14.

The timing circuit shown in FIGS includes components which provide apower supply circuit 112, a reset circuit 114, a timing circuit 116,andan output circuit '118. The power supply circuit 112 includes acapacitor" 1C, a capacitor 2C, a resistor 1R, a rectifying diode ID, aZener diode 2D and the resistor 82 which is mounted in the alcove 80.The capacitor 1C acts as a filter capacitor and is connected between alead l20 and a a junction 122. The lead is connected through the lead10611 to the terminal 74a. The terminal 740 is con nected through aswitch SW to a first side of an alternating current source S. The diode1D is connected between the junction 122 and a junction 124. Thejunction 124 is connected through the resistor 1R to a junction 126. Thejunction 126 is connected through the lead 10612 and terminal 74b to asecond side of the alternating current source S. The capacitor 2C isconspectively act as filter and noise suppressing'capa citors.

The resistor 1R limits the charging current of capacitor 1C and theresistor 82 acts as a dropping resistor.

The reset circuit includes transistors 1T, 2T and 3T, capacitors 3C and4C, resistors 2R-8R anda diode 3D. The transistors IT and 2T have theiremitters connected to the lead 120 and their collectors connectedthrough'resistors 6R and 7R respectively to the lead 130. The transistor3T has its emitter connected to the lead 130 and its collector connectedthrough the resistor 8R to a junction 132.'The resistors'ZR and 3R areconnected between the lead 120 and the junction 124 to act asvoltagedivider resistors. The base of the transistor IT is connectedthrough'the resistor 4R and the diode 3D to a junction between theresistors 2R'and 3R and the capacitor 3C is connected between the lead120 and a junction between the diode 3D and the resist tor 4R. The diode3D acts as a half waverectifier in the charging circuit for thecapacitor 3C. The resistor SR is connected between the base oftransistor IT and the lead 120 to act as a' bias resistor. The capacitor4C is connected between the base. of the transistor 3T and the lead 130as a noise suppressor. The bases of transistors 3T and 2T are connectedto the collectors of the transistors 2T and IT respectively.

The timing circuit includes a programmable unijunction transistor PT,resistors 9R-llR, capacitors 5C-6C, and the potentiometer resistor 78.The programmable'transistor PT has an anode A connected to the junction132, a gate g connected to a junction between the resistors 10R and 11R,which are connected between the leads 120 andl30, and a cathode Cconsistor 9R are connected in series between the junction 132 and thelead 120. The resistors 10R and 11R act as voltage dividers anddetermine the intrinsic stand-off noise suppressor and the resistor 9Rand the potentiometer 78 control the rate at which the timing capacitor5C is charged with the resistor 9R limiting the maximum rate at whichthe capacitor 5C charges.

The output circuit 118 includes a triac TR, a silicon controlledrectifier SR, a pilot light PL, a voltage suppressing diode D4, a Zenerdiode D5, capacitors 7C-9C and resistors l2R-l5R which are connected tocontrol the energization of the coil winding'54.

The term triac is an acronym that has been coined to identify the triode(three-electrode) A.C. semiconductor switch'which is triggered intoconduction by a gate signal in a manner similar to the action of an SCR.The triac, generically called a bidirectional triode thyristor, firstdeveloped by'General Electric (US. Pat. No. 3,275,909, and othersapplied for) differsfrom the SCR in that it can conduct in bothdirections of current flow in response to a positive or negative gatesignal.

The diode D4 is connected across the source S and acts as a transientvoltageclipper- The triac TR has a main terminal MTl connected to thelead 120 and a main terminal MT2 connected through the coil winding 54to the junction 126. The gate g of the triac TR is connected to ajunction 136. The capacitor 8C is connected between the junction 136 andthe lead 120 to suppress noise signals at the gate g of the triac TR.The Zener diode D5 has a cathode connected to the junction 136 and ananode connected to the anode of the controlled rectifier SR. Thecontrolled rectifier SR has a cathodeconnected through the resistor 13Rto the lead 130 and a gate connected to the junction 134. The capacitor7C and the resistor l2R are connected between the gate and the cathodeof the rectifier SR and act as noise suppressors and gate resistorsrespectively for the rectifier SR. The pilot light PL is preferably ofthe neon type and is connected in series with the resistor R. The seriesconnected pilot light PL and the resistor 15R are connected in parallelwith the triac TR and in parallel with the series connected capacitor 9Cand the resistor 14R which are also connected in parallel with thetriacTR for noise suppression.

All of the capacitors lC-9C aredischarged and all of the solid statecomponents'are nonconducting when the switch SW is open and the circuitis reset. The switch SW, when closed, connects the circuit including thelead 120 to the source S. The switch SW, when initially closed, causesthe capacitor 1C to be charged through the diode 1D and the Zener diodeD2, together with the capacitor 2C, causes the lead 120 to beapproximately volts positive in polarity relative to the lead 130. Thetransistor 1T conducts when the switch SW is closed and causes thetransistors 2T and 3T to be nonconducting. The nonconducting transistor3T permits the capacitor SC to be charged at a rate determined by theimpedance of the resistor 9R and the potentiometer 78. The voltagedivider provided by the resistors 10R and 11R determines-the intrinsicstandoff ratioof the programmable unijunction transistor PT. After apredetermined time interval, when the charge on the capacitor 5C reachesthe value dictated by the intrinsic stand-off ratio of the transistorPT, the transistor PT switches to its conductive state and supplies asharp voltage pulse through its anode'to cathode to the gate and cathodeof the rectifier SR. The rectifier SR is switched to its conductivestate by the voltage pulse and remains conducting as it is connectedacross the direct current source between the leads and 130.

The capacitor l C, the diode 1D and the Zener diode 2D rectify andfilter the alternating current output of the source S when the switch SWis closed and cause a direct current potential of approximately 20 vdcto be present between the leads 120 and 130. Thus when the rectifier SRconducts, a direct current will flow from the lead 120 through theterminal MTl to the gate g of the triac TR through a circuit thatincludes the Zener diode D5, the anode to cathode of the rectifier SR,the resistor 13R, the lead 130, the resistor 82, the diode 1D, thejunction 124 and the resistor 1R during the half cycle when the terminal74a is positive in polarity relative to the terminal 74b. During thehalf cycle when the source S causes the alternating potential at theterminal 74a to be negative relative to the terminal 7412, the charge onthe capacitor 1C causes the direct current to' continue to flow throughthe terminal MTl' and the gate g of the triac TR. The direct currentflow through the terminal MTl and the gate g of the triac TR switchesthe triac TR to a conductive state and causes alternating current toflow from the source S through the closed switch SW, the conductingtriac TR and the coil winding 54. The alternating current flow throughthe coil winding 54, as caused by the conducting triac TC, causes theelectromagnet assembly of the relay 10 to be energized and themovablecontact carrier to move upwardly and actuate the switchingcontactsof through the resistor 15R and the coil winding 54. The

current flowing through the coil winding 54 during periods when thepilot light PL is illuminated is insufficient to cause the electromagnetassembly of the relay to be energized to the degree necessary to causethe armature 32 to move into engagement with the magnet 30. Thus duringthe timing period the relay 10 will be de-energized and the pilot lightwill be illuminated and be visible through the lens 76 to indicate thepresence of the timing period and that the timing circuit is energized.At the end of the timing period, the triac TR conducts and provides alow impedance path in parallel with the pilot light PL and the resistor15R which causes the pilot light PL to be de-energized and not bevisible through the lens 76 to signal the end of the timing period.

The reset circuit 114 causes the capacitor SC to be rapidly dischargedwhen the switch SW is opened either during the timing period or afterthe timing period has ended and the relay 10 is energized. The'openingof the switch SW interrupts the circuit between the source S and thelead 120 and the junction 126 thereby causes the coil winding 54 to bede-energized and the armature 32 and the movable contact carrier 26 tomove to their de-energized positions. The opening of the switch SW alsointerrupts the charging circuit for the capacitor 3C and removes theemitter to base biasof the transistor lT so the capacitor 3C rapidlydischarges and the transistor 1T switches to its nonconductive state.The charging circuit for the capacitor 3C, that is connected between thelead 120 and the junction 124, includes'the diode D3 and the resistor3R. The bias circuit for the emitter tobase circuit of the transistor 1Tincludes the voltage divider resistors 2R and 3R which causes a currentflow in the base circuit of the transistor 1T that includes the resistor4R, the diode D3 and the resistor 3R. The removal of the potential onthe lead 120, when the switch SW is opened, causes the capacitor 3C torapidly discharge through the emitter to base of the transistor IT andthrough the resistor 5R.

The transistor 2T switches to a conductive state when the transistor 1Tswitches to a non-conductive state and the capacitor lC'is charged. Thecharge on the capacitor 1C causes base current flow in the transistor 2Tthrough a circuit that includes thelead 120, the emitter to base of thetransistor 2T, the resistor 6R, and the resistor 82. The emitter to basecurrent in the transistor 2T causes the capacitor l C to supply currentthrough the collector .of the transistor 2T and through the base andemitter of the transistor 3T whichcauses the transistor 3T to beconductive and the capacitor SC to rapidly. discharge through the lowimpedance circuit provided bythe conducting transistor 3T and theresistor 8R. Thus the timing capacitor 5C is rapidly dischargedimmediately after the switch SW is opened. In the embodiment shown, thecapacitorSC has a 47 MFD capacitance and the resistor 8R has a 100 ohmresistance which causes the capacitor to be discharged in approximately50 milliseconds. The rapid discharge of the capacitor 5C after theswitch SW opens prevents a buildup of a charge on the capacitor 5C andfalse energiza- .tion of thecoil winding 54 when the switch SW israpidly opened and closed before the end of a timing period and assuresthat-the timing circuit will have a high repeat accuracy when the switchSW is opened and im- 'mediately closed after the coil winding has'beenenergized in response to a timed-out timing period. The resistor 82 isprovided to limit the gate current in the triac TR to aminimum valuewhich will cause the triac TR to conduct'and therefore is mountedexternally of the housing 50 so the heat-generated in the resistor 82may be 'efficie'ntly dissipated by the cover 84.

While certain preferred embodiments of theinvention have beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

What is claimed is: 1. In an electromagnetically operated device, thecombination comprising: a base, an insulating stationary contact supportmounted on the base, a plurality of stationary contacts mounted on thesupport, a movable tioned onthe stationary magnet part for inducing amagnet flux in the stationary magnet part and the armature for causingthe armature and carrier to move from the firstposition to the secondposition a selected time interval after the coil assembly is energized,said coil assembly including a molded shell having a pair of spacedcavities, a projection extending upwardly ina first of said pair ofcavities from a bottom wall of the shell, a passage extended through theprojection, a coil winding positioned within the first cavity andsurrounding the projection, a pair of terminals having wire fasteningportions disposed externally of the shell and portions within a'secondof said pair of cavities, and means including electric circuit havingsolid state components positioned within the second cavity and connectedbetween the portions of the terminals within the second cavity and thecoil winding in the first cavity for delaying the energization of thecoil winding for a predeter' mined timed interval'when the electricpower is initially applied to the terminals. v

2. The combination as recited in claim. 1 including a thick-film boardand wherein the shell is formed of two parts which are secured togetherwith a first of said two shell parts providing the second cavity and ahousing for the thick-film board whereon components of the solid statecircuit are' carried and a second of the two shellparts providing thefirst cavity, a housingfor the coil winding, and a mounting for thefirst shell parts.

3. The combination as recited in claim 2 wherein the electric circuitincludes a potentiometer having a resistive portion positioned in thesecond cavity andan adjustment knob extending through a front wall ofthe first housing part so as to be externally accessible from a frontside of the device.

4. The combination as recited in claim 3 wherein the electric circuitincludes a light emitting device that is visible through an opening inthe front wall during the interval when the'electric circuit is delayingthe energization of the coil. 3

5. The combination as recited in claim 3 wherein the first shell partincludes an alcove extending in a top wall of the firstshell part andthe electric circuit includes a resistor which is heated when the pairof terminals are energized and is positioned in the alcove.

6. The combination as recited in claims including a metal. cover for thealcove. y

7. The combination as recited in claim 1 wherein the electric circuitincludes a timing capacitor which is charged at a predetermined ratewhen electric power is initially applied to the terminals, meansresponsive to the charge level on the capacitor'for causing the coil tobe energized when the charge on the capacitor reaches a predeterminedlevel and means for rapidly discharging the capacitor when the electricpower to the terminals is interrupted.

8. The combination as recited in claim 2 wherein the second shell partincludes an open sided cavity wherein the coil winding is positioned andthe cavity is filled with encapsulating material.

9. The combination as recited in claim 1 wherein the plurality ofstationary contacts are arranged as a row of spaced pairs of stationarycontacts'on the support and the movable contacts are arranged as a rowof spaced contacts on the carrier to individually bridge one of thepairs of stationary contacts.

10. The combination as recited in claim 1 wherein the stationarycontacts and-the movable contacts are arranged to selectively provide anormally open and .a

normally closed contact function. l=

1. In an electromagnetically operated device, the combinationcomprising: a base, an insulating stationary contact support mounted onthe base, a plurality of stationary contacts mounted on the support, amovable contact carrier, movable contacts positioned by the carrier toengage the stationary contacts and provide selected circuit opening andclosing functions when the carrier is moved from a first position to asecond position, an electromagnet assembly mounted on the base, saidelectromagnet assembly including a laminated magnet iron stationarymagnet positioned on the base, a laminated magnet iron armatureconnected to the carrier and movable between two positions relative tothe stationary magnet part for moving the carrier from the first to thesecond position and a coil assembly positioned on the stationary magnetpart for inducing a magnet flux in the stationary magnet part and thearmature for causing the armature and carrier to move from the firstposition to the second position a selected time interval after the coilassembly is energized, said coil assembly including a molded shellhaving a pair of spaced cavities, a projection extending upwardly in afirst of said pair of cavities from a bottom wall of the shell, apassage extended through the projection, a coil winding positionedwithin the first cavity and surrounding the projection, a pair ofterminals having wire fastening portions disposed externally of theshell and portions within a second of said pair of cavities, and meansincluding electric circuit having solid state components positionedwithin the second cavity and connected between the portions of theterminals within the second cavity and the coil winding in the firstcavity for delaying the energization of the coil winding for apredetermined timed interval when the electric power is initiallyapplied to the terminals.
 2. The combination as recited in claim 1including a thick-film board and wherein the shell is formed of twoparts which are secured together with a first of said two shell partsproviding the second cavity and a housing for the thick-film boardwhereon components of the solid state circuit are carried and a secondof the two shell parts providing the first cavity, a housing for thecoil winding, and a mounting for the fIrst shell parts.
 3. Thecombination as recited in claim 2 wherein the electric circuit includesa potentiometer having a resistive portion positioned in the secondcavity and an adjustment knob extending through a front wall of thefirst housing part so as to be externally accessible from a front sideof the device.
 4. The combination as recited in claim 3 wherein theelectric circuit includes a light emitting device that is visiblethrough an opening in the front wall during the interval when theelectric circuit is delaying the energization of the coil.
 5. Thecombination as recited in claim 3 wherein the first shell part includesan alcove extending in a top wall of the first shell part and theelectric circuit includes a resistor which is heated when the pair ofterminals are energized and is positioned in the alcove.
 6. Thecombination as recited in claim 5 including a metal cover for thealcove.
 7. The combination as recited in claim 1 wherein the electriccircuit includes a timing capacitor which is charged at a predeterminedrate when electric power is initially applied to the terminals, meansresponsive to the charge level on the capacitor for causing the coil tobe energized when the charge on the capacitor reaches a predeterminedlevel and means for rapidly discharging the capacitor when the electricpower to the terminals is interrupted.
 8. The combination as recited inclaim 2 wherein the second shell part includes an open sided cavitywherein the coil winding is positioned and the cavity is filled withencapsulating material.
 9. The combination as recited in claim 1 whereinthe plurality of stationary contacts are arranged as a row of spacedpairs of stationary contacts on the support and the movable contacts arearranged as a row of spaced contacts on the carrier to individuallybridge one of the pairs of stationary contacts.
 10. The combination asrecited in claim 1 wherein the stationary contacts and the movablecontacts are arranged to selectively provide a normally open and anormally closed contact function.